This invention pertains to curing of porous packs of impregnated material in an enclosed space such as a box.
In one of its more specific aspects, this invention relates to heat curing of binder-impregnated packs of fibrous material in an oven in which hot gas moving perpendicular to the pack is forced through the pack as the pack is conveyed through the oven.
Description of the invention is presented herein relative to mineral fibers such as glass fibers. However, the invention is applicable to any porous material through which gas is forced in an enclosed space.
Forming glass fibers, impregnating the fibers with a binder, collecting the fibers into a pack on a forming conveyor or chain, compressing the uncured pack to the desired thickness or height, and conveying the compressed pack through a curing oven while passing hot gas perpendicularly through the pack to cure the binder, are well-known. Products made in this fashion comprise thermal insulation and ceiling panels.
The curing oven usually comprises two flat, foraminous, moving, endless conveyor belts, one located parallel to and above the other, which belts travel lineally through the oven so that the pack is moved by, between, and in constant contact with both belts. The thickness of the cured pack is determined by the distance between the flat, facing surfaces of the belts. This distance, called the bridge height, is adjustable to facilitate production of varying pack thicknesses. The bottom belt elevation relative to the oven structure is fixed; the top belt elevation, or bridge height, is adjustable.
The foraminous conveyor belts usually comprise a series of foraminous slats, or flights, which are fixed to a pair of conveyor chains. The flights are fitted across the chains, side-by-side in contact relationship. A blower pressurizes the back side of one of the conveyor belts so that hot gas is forced through the foraminous flights, through the pack, then through the opposing flights.
The hot gas driven by the blower is forced through the pack in a direction perpendicular to the pack surface in contact with the flights. However, because the sides of the conveyor belt system are open to the interior of the oven, a significant portion of the hot gas is forced through the pack edges, bypassing the opposing flights. This can cause the edges of pack to overcure, to burn, and to be eroded. Attempts to solve this bypass problem have involved placement of metal brushes between the top conveyor belt, or bridge, and the oven shell sides. Because the bridge must move up and down inside the oven shell to change the pack thickness, the brushes must move up and down in contact with the oven shell. Because the oven shell inner surface is not a plane, mainly because of the discontinuities occasioned by the cleanout doors on the oven sides, the brushes cannot bear continuously on the oven shell at all bridge settings. Accordingly, use of brushes was not a satisfactory solution to the bypass problem. The invention described herein impedes hot gas bypass flow, promoting even, complete, and appropriate degree of cure, without pack edge overcure, burn, or erosion. The apparatus of this invention is durable, heat resistant, and is not dependent upon a mating seal with the oven shell sides for operability. The apparatus seals pneumatically the pack-curing space between the belts from the oven shell space. Sealing pneumatically is defined as employment of a sealing apparatus capable of impeding or prohibiting movement of gas from one space to another.
It is possible to use both the brushes and the apparatus of this invention simultaneously to control curing gas bypass.